Control of five-level flying capacitor based active-neutral-point-clamped converter for grid connected wind energy applications

Integration of wind energy sources into the distribution grid affects the voltage profile that could be stabilized through the grid reinforcement or limiting the active power injection. This paper presents a control strategy to regulate the voltage at point of common coupling (PCC) through reactive power exchange to the grid. The reactive power capability of the grid-connected hybrid multilevel converter is based on the voltage sensitivity of the distribution grid at PCC. A hybrid five-level multilevel converter referred as flying capacitor (FC) based active-neutral-point-clamped (ANPC) converter is considered. It is an arrangement of a three-level ANPC converter and a two-level cell. Also, a control strategy is proposed to regulate the FCs voltages of the grid-connected hybrid multilevel converter at their required values. The proposed FC control strategy provides extra freedom to regulate the dc-link capacitor voltages with dc-offset injection technique. Simulation studies demonstrate the performance of the proposed control strategies for the system considered.